Electrophotographic printing machines such as copiers and printers have become common place. In such machines a photoconductive surface is charged to a substantially uniform potential. That surface is then exposed to light to record an electrostatic latent image which corresponds to the information to be marked onto a substrate. Thereafter, a developer comprised of charged powder toner particles is transported into contact with the electrostatic latent image. Those toner particles are attracted onto the latent image to form a toner powder image. That powder image is then transferred from the photoconductive surface onto a substrate and then fused (permanently affixed) to the substrate using heat and pressure.
The foregoing generally describes a typical black and white electrophotographic printing machine. Electrophotographic printing can also produce color images by repeating the above process for each color of toner that is used to make the color image. For example, the charged photoconductive surface may be exposed to a light image which represents a first color, say black. The resultant electrostatic latent image can then be developed with black toner particles to produce a black image which is subsequently transferred to a substrate. The process is then be repeated for a second color, say yellow, then a third color, say magenta, and finally a fourth color, say cyan. Beneficially each color toner image is transferred to the substrate in superimposed registration so as to produce the desired composite toner powder image on the substrate.
The color printing process described above superimposes the various color toner powder images directly onto a substrate. Another color printing process uses an intermediate transfer belt. In such systems successive toner powder images are transferred in superimposed registration from the photoconductor onto the intermediate transfer belt. Only after the composite toner powder image is formed on the intermediate transfer belt is the composite toner powder image transferred to the substrate and fused.
Developing materials are usually comprised of not only toner particles but also carrier granules. In practice, the toner particles triboelectrically adhere to the carrier granules until the toner powder particles are attracted to the latent image on the photoconductor. An alternative to such powder developing materials are liquid developing materials.
Liquid developers, also referred to as liquid inks, use a liquid carrier into which the toner particles are dispersed. When developing with liquid developers both the toner particles and the liquid carrier are advanced into contact with the electrostatic latent image. Of course after the liquid developer is deposited on a receiving surface that surface is wet with the liquid carrier. Since it is usually undesirable to deposit liquid onto most substrates, systems which use liquid developers generally use an intermediate transfer member which receives and drys the liquid image before transferring the image onto a substrate.
Heating the intermediate transfer member would be advantageous since it would tend to drive off the liquid carrier and leave behind a coagulated toner image. However, it is important that the intermediate transfer member is not overheated and that it is cool before the next liquid image is received. In the prior art the requirements of receiving the liquid developer on a cool surface and driving off the liquid carrier without damaging either the intermediate transfer member or the photoconductive surface while achieving high quality images from a fast printing machine were difficult to achieve simultaneously. Thus, inventive apparatus and methods which enable fast localized heating of intermediate transfer members and/or of liquid carriers while having a relatively cool intermediate transfer member where toner images are received from a photoconductive surface would be beneficial.
Various approaches have been devised to produce multicolor color copies. The following disclosures may be useful references: